(1) Field of the Invention
The present invention relates to an optical interconnection circuit structure, and more particularly to an optical interconnection circuit structure in which semiconductor optical devices are mounted and optical waveguide circuits and formed on a common substrate.
(2) Description of the Related Art
The maximum capacity of optical communication systems is advancing and, at the same time, in pursuing high level multifunctional systems, there are strong demands for optical fiber networks which are small, of low cost, highly integrated and highly functional. This means that it is essential for the optical devices for equipment such as optical transmission equipment and optical receiving equipment to also be small, highly integrated and of low cost.
Current practices provided for optical transmission and optical receiving equipment utilize a structure whereby a lens is set up between the optical fiber and either the semiconductor light source or the semiconductor light detector and optical connection is via space. This construction involving a lens and optical connection via space is referred to as "micro-optics". In micro-optics constructions there are difficulties whereby, for example, the lens shape and the shape of the package for the semiconductor light source and the semiconductor light detector restrict how small the construction can be made. Also, in order to have an efficient joint or connection between the optical fiber and the light detector using light in space, it is necessary to align the optical axis very precisely. As this operation demands many fabrication steps in the present circumstances, the cost of this cannot be reduced. Needless to say that this is completely unsuitable for high integration of similar functions or functions of a different variety.
Recently, it has become necessary to enhance bidirectional communication systems, and it is hoped to bring these systems even into the household. At this time, to make this bidirectional communication possible, it is necessary to have an optical device with optical transmission equipment and optical receiving equipment but, if these are constructed individually, the optical transmitting and receiving apparatus is cumbersome and system propagation is hindered. Therefore, although an optical device which incorporates the two functions in one body is preferable, it is difficult to realize this with a micro-optics structure for the above mentioned reasons. With this as background, Henry et al reported their research for "Light Wave Technology" in IEEE (pp. 1530-1539 (1989)) aiming for a smaller, more highly integrated lower cost structure using optical waveguide.
A conventional optical interconnection circuit structure is shown in a schematic plan view in FIG. 1. In the structure shown therein, formed on a substrate 1 are optical waveguides 2, 2a including a splitter function circuit 7. These optical waveguides 2, 2a, a semiconductor light source and the semiconductor light detector for signal detection are respectively and directly coupled optically on the same substrate 1. In FIG. 1, a semiconductor light detector 5a for monitoring the light output from the semiconductor light source 4 is also integrated on the same substrate 1 and is optically coupled with the waveguide 2b, but even if the semiconductor light detector 5a for monitoring the light output from the semiconductor light source 4 is not present, there will still be no problems with the functioning of the transmitting and receiving equipment for bidirectional optical communication. Also, the electronic reception device (not shown) for the semiconductor light detectors 5 and 5a is integrated on the same substrate 1 but even if this electronic device is not on the same substrate, there will still be no problems with the functioning of the transmitting and receiving equipment for bidirectional optical communication. With the optical waveguide 2 as shown in FIG. 1, a small size optical transmitting and receiving device can be achieved. The optical waveguide itself is suitable for mass production using lithographic processes, thus reducing the cost of production.
The semiconductor optical element mounted on the substrate and the optical waveguide formed on the substrate are optically interconnected on the substrate. In order to connect the optical waveguide and the semiconductor optical element optically in an efficient manner in the optical interconnection circuit in which the semiconductor device is fixed to the substrate, it is necessary to adjust the optical axis of the optical waveguide and the semiconductor optical element within all three dimensions to an accuracy of within 1 .mu.m. However, doing this demands a high level of precision when adjusting the optical axis and as this operation requires a large number of fabrication steps, costs cannot be reduced according to the present technology. Consequently, there has yet to be realized a semiconductor optical interconnection fixing means which can overcome the structural problems in a conventional means for optically connecting a semiconductor optical element placed on the substrate with an optical waveguide formed on the substrate and which is simple and yet highly efficient and reliable.